1. Field of the Invention
The present invention relates to a display device. The invention particularly relates to an IPS liquid crystal display device in which the reliability of a seal portion is improved.
2. Description of the Related Art
A liquid crystal display device includes a TFT substrate having pixel electrodes, thin film transistors (TFT), or the like formed thereon in a matrix form, and a counter electrode opposing the TFT substrate and having color filters, or the like formed at positions corresponding to the pixel electrodes of the TFT substrate. Liquid crystal is put between the TFT substrate and the counter substrate. The liquid crystal display device controls light transmittance for each pixel by using liquid crystal molecules to form images.
Since the liquid crystal display devices are flat and light in weight, their application has been generalized in various fields including large-sized display devices such as television sets, mobile phones, DSCs (Digital Still Cameras), or the like. In contrast, the liquid crystal display devices involve a problem in terms of viewing angle characteristics. The viewing angle characteristics are a phenomenon that the brightness or chromaticity changes between when a screen is observed from the front and when the screen is observed in the oblique direction. The IPS (In Plane Switching) mode of operating liquid crystal molecules by a horizontal electric field has satisfactory viewing angle characteristics.
In the IPS mode, preferred characteristics are obtained when a pre-tilt angle is not formed with respect to liquid crystal molecules near an alignment film. Accordingly, it is advantageous to form the axis of orientation for the alignment film not by a rubbing method but by an optical alignment method. The optical alignment method also has an advantage over the rubbing method in that static electricity is not generated.
In optical alignment method, a polarized UV light is radiated to an alignment film, and thereby, such anisotropy that liquid crystal molecules are aligned in a predetermined direction, is provided to the alignment film. JP-A-2005-351924 describes a technique relating to such optical alignment.